Photocatalytic properties of screen-printed titania

Nanocrystalline thin films of important surface roughness and complexity were prepared by screen-printing of commercial TiO₂ powder. The screen-printed titania films were tested in the photocatalytic decomposition reaction of methyl orange under UV light (350 nm). The photocatalytic activity strongly depends on the titania paste components and especially on the presence of a surface modifier (acetyl acetone) combined with a rheology controlling agent (ethyl cellulose). This results in improvement of the paste viscosity and optimization of the films morphology. Experiments under direct full sunlight illumination prove the importance of the screen-printed films for practical applications.     

Optimization of screen-printing parameters of SN9000 ink for pinholes using Taguchi method in chip on film packaging

The influence of pinholes on the chip on film (COF) in screen-printing was studied in this paper. Yield improvement is the most challenging part of COF manufacturing in view of its processing complexity, mainly in the screen-printing process. The process parameters such as ink capacity, origin control distance, angle of the squeezer, method of mixing, freshness of ink, speed of printing, and speed of scraper are considered to improve the pinholes. In Taguchi method, a two level orthogonal array is used to determine the signal-to-noise (S/N) ratio. Analysis of variance and the F-test values are used to determine the most significant process parameters affecting the pinholes. Confirmation analysis tests with the optimal levels of process parameters are carried out. The results of the experiment show that Taguchi method is a very suitable approach with regard to solving quality problems related to such pinholes.     

CuO formation control as a function of mixed ratio of Cu-free powders in the synthesis of YBCO superconductors on Cu substrates

YBa₂Cu₃O_x (Y123) superconducting films were fabricated on Cu substrates using a simple screen-printing method, from Cu-free powders (Y₂O₃ and BaCO₃). In the process, CuO, which causes superconducting properties of Y123 films to deteriorate, was formed on the film surface. By varying the atomic ratio of Y to Ba (Y:Ba = 1:1∼1:4), the ratio needed to prevent CuO formation was found for the film surface that had been heat-treated at 980^∘C for 17 s. The film, with the ratio of Y to Ba (Y:Ba = 1:1), is reheat-treated at 930^∘C for 9 min 30 s to form a superconducting Y123 phase. It was possible to prevent CuO formation by controlling the ratio of Cu-free powders in the mixture and to fabricate YBCO superconductors on Cu substrates using a two-step heat-treatment.     

Portable,parallel grid dye-sensitized solar cell module prepared by screen printing

Screen-printing technology is used to fabricate large dye-sensitized solar cells (DSSCs). The high series-resistance associated with transparent conductive oxide glass substrates causes poor performance in large DSSCs especially at an exposure of 1 sun. The DSSC design has an embedded silver grid; a fluorine-doped tin oxide (FTO) glass substrate and stripe type titanium dioxide (TiO₂) active layers introduced by screen-printing. The counter electrode is prepared from a screen printable paste based on hexachloro platinic acid. A DSSC module, which consists of five stripe-type working electrodes on a 5 cm × 5 cm, embedded silver grid FTO glass substrate, shows stable performance with an energy conversion efficiency of 5.45% under standard test conditions.     

Investigation into real-time pressure sensing properties of SnO2, TiO2, and TiO2/ZnO thick films with interdigitated electrodes

The pressure sensing properties of nanocomposite SnO₂, TiO₂, and TiO₂/ZnO thick film capacitors with interdigitated electrodes are investigated. To form the dielectric layers, the metal oxides powders were respectively mixed with isopropanol, wet ball milled for 24 h, then the mixtures were dried at 120 °C and further the powders were placed under 2 tonnes of pressure to form pellets, which were fired at 1250 °C (rate of 5 °C/min) in a vacuum of 6 × 10⁻³ mbar for 5 h, followed by cooling (rate of 3 °C/min). After firing, the resultant nanopowders were mixed with 7 wt.% of polyvinyl butyral (binder) and suitable amount of ethylenglycolmonobutylether (solvent) to form the pastes. These were screen-printed over the Ag electrodes on alumina substrates to form SnO₂, TiO₂, and TiO₂/ZnO capacitor pressure sensors accordingly. The evaluation of pressure sensing properties of these sensors was performed using a HP 4192A Impedance Analyser, which recorded the changes in the values of the capacitances under different mechanical stresses. At the applied load of 5 kPa, the response times of 2.5 s, 5.6 s and 4 s were recorded for SnO₂, TiO₂, and TiO₂/ZnO sensors, respectively. In addition to instant response times, these pressure sensors have the advantage of being reusable, as their electrical properties were restored to the original value after annealing for 2 h at 80 °C. Moreover, one year later after the initial testing, the sensors were still operational and produced similar time responses to pressure.     

A screen-printed interdigitated back contact cell using a boron-source diffusion barrier

A low-cost approach to fabricating interdigitated back contact cells is carried out on the principle of screen-printing a material that serves both to dope the rear surface and as a diffusion barrier to the dopant species of the opposite polarity. With this technique, an interdigitated pattern of n⁺ and p⁺ regions is formed on the cell back. Shunt-free rear interdigitated junctions are achieved. This work produced a cell with confirmed conversion efficiency of 10.5%. Areas for further efficiency gains are discussed.     

Fabrication of field emission display prototype utilizing printed carbon nanotubes/nanofibers emitters

Carbon nanotubes/nanofibers (CNTs) used as emitters, diode-type field emission display (FED) prototypes of dot matrix and character images were fabricated by low-cost techniques and equipments, respectively. The technical development in the design and fabrication of the cathode, the anode, and the panel, is described. CNTs were produced by a simple, low-cost and easily-controllable thermal chemical vapor deposition. The cathode was prepared by the screen-printing method. The field emission characteristics were enhanced by a heat post-treatment in H₂ gas atmosphere. The panel structure was packaged by a vacuum fluorescent display-like process and vacuum-sealed through an exhaust glass tube. The fully-sealed CNTs FED (c-FED) showed good emission properties. The brightness of 600 cd/m² was achieved from the yellow phosphor at a relatively low applied electric field. The developed technology has a potential practical application in c-FED.     

Screen-printing fabrication of electrowetting displays based on poly(imide siloxane) and polyimide

We report a screen-printing fabrication process for large area electrowetting display (EWD) devices using polyimide-based materials. The poly(imide siloxane) was selected as hydrophobic insulator layer, and relatively hydrophilic polyimide as grids material. EWD devices that use poly(imide siloxane) as hydrophobic insulator fabricated with conventional methods showed good and reversible electrowetting performance on both single droplet level and device level, which showed its potential application in EWDs. The compatibility of polyimide-based materials (hydrophobic poly(imide siloxane) and hydrophilic polyimide) guarantee the good adhesion between two layers and the capability of printable fabrication. To this end, the hydrophilic grids have been successfully built on hydrophobic layer by screen-printing directly. The resulting EWD devices showed good switch performance and relatively high yield. Compared to conventional method, the polyimide-based materials and method offer the advantages of simple, cheap and fast fabrication, and are especially suitable for large area display fabrication.     

Integration of 2D printing technologies for AV2O6 (A=Ca,Sr, Ba)-MO (M=Cu,Ni, Zn) photocatalyst manufacturing to solar fuels production using seawater

The non-polluting nature of photocatalytic H₂ production makes of interest the study of semiconductors for this process. Scale-up of the photocatalytic hydrogen process to a pilot plant requires the photocatalyst's immobilization to enhance the charge transfer and facilitate its recovery. In this work, screen-printed films from the AV₂O₆ (A = Ca, Sr, Ba) semiconductor family were fabricated and evaluated in photocatalytic water splitting for H₂ production in distilled water and seawater under UVA light. The films exhibited ∼3.1 eV band gaps, high crystallinity, and heterogeneous morphologies. BaV₂O₆ film exhibited the highest H₂ production in distilled water (691 μmol/g), related to the synergistic effect between a higher crystallinity and traces of V⁺⁴ species that decrease the recombination of the photogenerated charges. Also, to take advantage of the dissolved species in seawater that could act as sacrificial agents, the BaV₂O₆ film was evaluated in seawater, in which H₂ production was up to 6 times higher (4374 μmol/g) than in distilled water. The BaV₂O₆ film was decorated with simple oxides (CuO, NiO, and ZnO) by the ink-jet printing technology to increase its photocatalytic performance for H₂ production. The highest efficiency with distilled water was obtained with the BaV₂O₆-CuO film, which reached an H₂ production up to 30 times higher than the bare BaV₂O₆, own to the n-p heterostructure formation that enhances the charge transport in the photocatalytic process. When the BaV₂O₆-CuO film was evaluated in seawater, a more constant H₂ production was observed; moreover, the efficiency was similar compared to the production in distilled water (20,563 μmol/g). To elucidate the seawater compounds that most influence the H₂ production, a two levels Plackett–Burman experiments design was carried out in simulated seawater. The analysis revealed that the SO₄²⁻ ions from the CaSO₄ could be decreasing the H₂ production by acting as Lewis's acid sites that trap the photogenerated e⁻ competing for its usage with the H⁺. Additionally, the Cl⁻ ions and the HCO₃⁻ reduction improved the HCOOH production from simulated seawater, reaching 26 times a higher production (23,333 μmol/g) than in distilled water.